Question

PEDIGREE ANALYSIS Cystic fibrosis is a recessive inherited disorder that affects one in 2,500 people of European descent. People afflicted with this condition have defective or absent protein channels which causes an accumulation of extracellular chloride ions, leading to a buildup of mucus around the lungs and digestive system. This sticky mucus clogs the lungs leading to life-threatening lung infections, and also obstructs the pancreas and causes poor absorption of food. With treatment, individuals can live into their 30's and 40's, giving them the opportunity to have children and live normal lives. The pedigree below shows four generations of the Smith family, who have had many members afflicted with cystic fibrosis. Cystic Fibrosis - Recessive Disorder The Smith Family Tree 9 49 040900700 000 KEY NN = Normal Nn = Normal nn = Has cystic fibrosis 0 - Normal female - Normal male O : Female with CF - Male with CF What are the possible genotypes of the following individuals in this family? IV-6 1-2_ - 5 I-3_ IV-5 III-14 125

Answer 1

Cystic Fibrosis is an autosomal recessive disease, so to solve pedigree questions we have to learn some concept-

for autosomal recessive inheritance-

1-traits often skip generations

2- if both parents are affected, all children should be affected

3- if normal person mates with affected person all children produced will be unaffected but if atleast one child is affected indicates that normal parent is heterozygous.

Goross between normal heterozygous. Nn Nn NN NN Nn nn hoss between Nosimal heterozygous and affected Brodices half of Nn Ton Normal and half of tected PTT children Nn Nn nn nn

Now in this question it is given that normal person have genotype NN or Nn and person affected with cystic fibrosis have genotype nn, so all the affected person i.e. 2, 4, 8 of generation II, 2,3,7,12,14 of generation III and 4,6,8and 10 of generation IV have genotype nn

in 1st generation cross between unaffected 1 and 2 produces affected and unaffected child that is the 1 and 2 are heterozygous with genotype Nn

in generation II cross between normal 1, 5, 9 and affected 2, 4, 8 respectively produces both normal and affected children it means 1,5 and 9 are heterozygous Nn and all the normal children have genotype Nn and affected genotypes is nn in III generation

cross between normal 6 and 7 produces normal children it means their genotype will be NN or Nn

In III generation cross between normal 4 and 5 produces normal children it means there genotype is NN or Nn.

now

I-1 Nn

I-2 Nn

IV-1 NN or Nn

IV-5 Nn because according to point 3 given above if cross between normal and affected person produces all the normal children then the genotype of normal parent will be NN but if atleast one child is affected then genotype of normal parent will be Nn

II-6 NN or Nn

IV- 6 nn

III-5 NN or Nn

II-3 NN or Nn

III-14 nn

III-1 Nn